Many hydrocarbon refining processes require water intake (excluding once-through cooling water) that is free of salts and suspended solids and the amount of water required for refinery operations is large: typical refineries might, for example, require from about 25,000 to about 150,000 m3/day. River water and sea water as well as recycled municipal waste water may be used as sources for the required amounts of water and with the amounts of dissolved salts and suspended solids typically encountered with such sources, a heavy load is imposed on water purification plants. A typical refinery limitation on the total dissolved solids (TDS) in bulk waste water can be as low as 2,000 wppm. While filtration, for example, through sand beds, may be effective to remove suspended solids, removal of the dissolved salts presents more difficult problems. Water purification by reverse osmosis or evaporation is an energy intensive process and with recent increases in the cost of energy, by a factor of approximately three since the year 2000, reliance on conventional source becomes progressively less tenable.
Solar power has been proposed for desalination using either flat panel evaporators as in U.S. Pat. No. 5,672,250 or concentrated solar power as described in U.S. Pat. No. 5,645,693. Solar energy, plentifully available in certain areas of the world, has been proposed both for the generation of electrical energy and for the provision of potable water. See, for example, “Concentrating Solar Power for Seawater Desalination”, Trieb, MENAREC 4, 20-24 Jun. 2007, estimating that the solar energy received on each square kilometer of desert land in the MENA region is sufficient to desalinate 165,000 m3/day of water, making such a plant capable of supplying the fresh water requirements of even a large petroleum refinery.
Refinery cooling tower systems will typically impose a concentration limit on total dissolved salts (TDS) of about 55,000 wppm at 50° C.; in the case of a typical seawater with 30,000 or 35,000 to 40,000 wppm TDS, repeated recycling through the cooling tower with these levels of dissolved salts cannot be accepted without resort to high blowdown rates. In addition, care must be taken in selecting the intake location to assure that the suspended solids do not exceed 200 wppm in the recirculated water.
The use of concentrated solar power or nuclear thermal energy presents an attractive option to the problem of providing desalinated water in large quantities for use in petroleum refineries. The primary advantages of using solar thermal or nuclear heat purified water in refining processes are:                a) fossil fuels such as natural gas or refined crude oil are not combusted for providing heat to the water purification process, thus leading to conservation of fossil fuel resources,        b) the carbon footprint of water purification is significantly reduced,        c) solar thermal or nuclear heat is available in sufficient quantity and quality to provide for water heat from the water purification to be utilized for other purposes.        